Well i did GCSE french, not at A level anymore but i some how got full marks in my oral at gcse. anyway, what we was told to do was basically write out an amazing speech and *literally* remember of by heart and just keep doing it over and over again, and then add more flare and proper confidence to it. I think even if your blagging it, i think the tone and confidence in your voice is so important, because at the end of the day, teh examiner can only hear your voice, so i guess if they can "feel" your confidence in your voice then thats a major plus.
for questions and stuff off the cuff, just try and think about all the vocab you go through in your class, the sentences, the topics etc, and let those ideas just expand and "snowball" in your head.
anyway, hope thats alright x